Los Angeles police are investigating several unlicensed marijuana shops they believe are engaging in criminal activity.

During a news conference, LAPD Deputy Chief John Sherman said he believes there are hundreds of those businesses operating around L.A.

"We have several hundred, probably somewhere in the neighborhood of 200 to 300, of what we believe are these unlawful and illegal establishments operating throughout the city," he said.

Authorities said a marijuana business on Laurel Canyon and Van Nuys boulevards in Pacoima has been a trouble spot for years. Police arrested three people during a raid at the shop last week, including a convicted felon who was in possession of a weapon.

"A person was operating as a security guard. That person was unlicensed. That person was armed. We recovered three firearms out of that location," Sherman said.

Police have identified 18 businesses in the city that they suspect are associated with criminal activity.

Officials said unlawful pot operations contribute to crime in the surrounding communities.